CIDR to IP Range and IP Range to CIDR Converter (IPv4 and IPv6)

This CIDR to IP range converter expands CIDR blocks into their first and last address and host count, turns any IP range into the smallest set of CIDR blocks, and lists every address in a block, for IPv4 and IPv6. It runs entirely in your browser: nothing you type is sent to our server.

Three modes

• CIDR → range: network, last address, usable host range, number of addresses and hosts, netmask and wildcard for each block. Lines with host bits set (198.51.100.17/28) are rounded to the network (198.51.100.16/28).
• Range → CIDR: the minimal list of blocks that covers exactly a start-end range, for example 192.0.2.10 – 192.0.2.200 needs 8 blocks.
• List every IP: all addresses in a block or range, up to 65,536 (a /16), with a download.

Block rules for your server

Choose an output format to turn the blocks into rules you can paste: CSF (csf -d or csf.deny lines), nginx deny, Apache Require not ip, iptables/ip6tables or an nftables set. Check the ranges first: blocking a provider’s whole range can also block real users and search engines.

Usable hosts

In IPv4 the first (network) and last (broadcast) address of a subnet are not usable for hosts, except in /31 point-to-point links (RFC 3021) and /32 single hosts. IPv6 has no broadcast address, so every address in the block is counted.

For subnet planning with a visual bit map, see our IP subnet calculator; for many networks into one summary route, see the route summarization calculator.

How we checked it

We compared the address library behind this tool with Python’s ipaddress module on 1,105 random cases (range to CIDR, merging, IPv6 formatting, invalid input) with no differences, then checked the page in Chromium on desktop and phone widths.

Frequently asked questions